FIGURE 6-2 Population potentially at risk from excessive nutrient intakes. The fraction of the population consistently consuming a nutrient at intake levels in excess of the Tolerable Upper Intake Level (UL) is potentially at risk of adverse health effects. Additional information is necessary to judge the significance of the risk.

some portion of the population has intakes above the UL, a risk may exist and the need to take action to reduce population intakes should be evaluated. For example, the UL for niacin for adults is 35 mg/day. The LOAEL for niacin is 50 mg/day and the uncertainty factor is 1.5 (indicating a good level of confidence in the data). The adverse effect noted is a relatively benign vasodilation causing flushing of the skin that may be accompanied by a burning, itching, or tingling sensation; this effect is readily reversible by a reduction in intake. The UL for vitamin B₆ is 100 mg/day for adults and the NOAEL is 200 mg/day with a UF of 2. The adverse effect observed—sensory neuropathy—is a serious and irreversible condition. Therefore, public health concern over a segment of the population routinely consuming niacin in excess of the UL would not be as great as if a segment of the population were routinely consuming vitamin B₆ in excess of the UL.

Figure 6-3 illustrates a situation in which usual dietary intake from foods represents no discernible risk but the addition of intakes from supplement usage makes a fraction of the population potentially at risk. Figure 6-4 represents the type of analysis that would apply when